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We study the problem of constructing explicit sparse graphs that exhibit strong vertex expansion. Our main result is the first two-sided construction of imbalanced unique-neighbor expanders, meaning bipartite graphs where small sets…

Combinatorics · Mathematics 2024-01-17 Jun-Ting Hsieh , Theo McKenzie , Sidhanth Mohanty , Pedro Paredes

We present a new explicit construction of onesided bipartite lossless expanders of constant degree, with arbitrary constant ratio between the sizes of the two vertex sets. Our construction is simpler to state and analyze than the only prior…

Combinatorics · Mathematics 2024-01-10 Louis Golowich

In this note, we give very simple constructions of unique neighbor expander graphs starting from spectral or combinatorial expander graphs of mild expansion. These constructions and their analysis are simple variants of the constructions of…

Computational Complexity · Computer Science 2024-01-29 Swastik Kopparty , Noga Ron-Zewi , Shubhangi Saraf

We present the first explicit construction of two-sided lossless expanders in the unbalanced setting (bipartite graphs that have polynomially many more nodes on the left than on the right). Prior to our work, all known explicit…

Computational Complexity · Computer Science 2025-02-11 Eshan Chattopadhyay , Mohit Gurumukhani , Noam Ringach , Yunya Zhao

We construct an infinite family of bounded-degree bipartite unique-neighbour expander graphs with arbitrarily unbalanced sides. Although weaker than the lossless expanders constructed by Capalbo et al., our construction is simpler and may…

Combinatorics · Mathematics 2023-01-10 Ron Asherov , Irit Dinur

We give the first construction of explicit constant-degree lossless vertex expanders. Specifically, for any $\varepsilon > 0$ and sufficiently large $d$, we give an explicit construction of an infinite family of $d$-regular graphs where…

Combinatorics · Mathematics 2025-04-22 Jun-Ting Hsieh , Alexander Lubotzky , Sidhanth Mohanty , Assaf Reiner , Rachel Yun Zhang

An undirected graph is said to have \emph{unique neighborhoods} if any two distinct nodes have also distinct sets of neighbors. In this way, the connections of a node to other nodes can characterize a node like an "identity", irrespectively…

Combinatorics · Mathematics 2025-05-13 Stefan Rass

A graph $G=(V,E)$ is called an expander if every vertex subset $U$ of size up to $|V|/2$ has an external neighborhood whose size is comparable to $|U|$. Expanders have been a subject of intensive research for more than three decades and…

Combinatorics · Mathematics 2019-01-29 Michael Krivelevich

We study connections between expansion in bipartite graphs and efficient online matching modeled via several games. In the basic game, an opponent switches {\em on} and {\em off} nodes on the left side and, at any moment, at most $K$ nodes…

Data Structures and Algorithms · Computer Science 2024-07-09 Bruno Bauwens , Marius Zimand

We construct the first explicit two-sided vertex expanders that bypass the spectral barrier. Previously, the strongest known explicit vertex expanders were given by $d$-regular Ramanujan graphs, whose spectral properties imply that every…

Combinatorics · Mathematics 2024-11-19 Jun-Ting Hsieh , Ting-Chun Lin , Sidhanth Mohanty , Ryan O'Donnell , Rachel Yun Zhang

In this survey we aim to give a comprehensive overview of results using sublinear expanders. The term sublinear expanders refers to a variety of definitions of expanders, which typically are defined to be graphs $G$ such that every…

Combinatorics · Mathematics 2024-09-16 Shoham Letzter

We study the classical expander codes, introduced by Sipser and Spielman \cite{SS96}. Given any constants $0< \alpha, \varepsilon < 1/2$, and an arbitrary bipartite graph with $N$ vertices on the left, $M < N$ vertices on the right, and…

Information Theory · Computer Science 2022-01-11 Xue Chen , Kuan Cheng , Xin Li , Minghui Ouyang

An infinite family of bounded-degree 'unique-neighbor' expanders was constructed explicitly by Alon and Capalbo (2002). We present an infinite family F of bounded-degree unique-neighbor expanders with the additional property that every…

Combinatorics · Mathematics 2016-05-11 Oren Becker

A graph with vertex set V and edge set E is called a (d,c)-expander if the maximum degree of a vertex is d and, for every subset W of V that has cardinality at most |V|/2, the number of edges between vertices in W and vertices outside of W…

Combinatorics · Mathematics 2007-05-23 Lars Engebretsen

This paper introduces an extended notion of expansion suitable for radio networks. A graph $G=(V,E)$ is called an $(\alpha_w, \beta_w)$-{wireless expander} if for every subset $S \subseteq V$ s.t. $|S|\leq \alpha_w \cdot |V|$, there exists…

Data Structures and Algorithms · Computer Science 2018-02-21 Shirel Attali , Merav Parter , David Peleg , Shay Solomon

Bauwens and Zimand [BZ 2019] have shown that lossless expanders have an interesting online matching property. The result appears in an implicit form in [BZ 2019]. We present an explicit version of this property which is directly amenable to…

Data Structures and Algorithms · Computer Science 2021-02-17 Marius Zimand

In this paper we show that graphs of "neighbourly" cubical complexes -- cubical complexes in which every pair of vertices spans a (unique) cube -- have good expansion properties, using a technique based on multicommodity flows. By showing…

Combinatorics · Mathematics 2007-05-23 Thomas Voigt

Deterministic constructions of expander graphs have been an important topic of research in computer science and mathematics, with many well-studied constructions of infinite families of expanders. In some applications, though, an infinite…

Data Structures and Algorithms · Computer Science 2015-07-07 Michael Dinitz , Michael Schapira , Asaf Valadarsky

We develop a new approach for approximating large independent sets when the input graph is a one-sided spectral expander - that is, the uniform random walk matrix of the graph has its second eigenvalue bounded away from 1. Consequently, we…

Data Structures and Algorithms · Computer Science 2024-11-07 Mitali Bafna , Jun-Ting Hsieh , Pravesh K. Kothari

Let $G=(V,E)$ be a finite graph. For $v\in V$ we denote by $G_v$ the subgraph of $G$ that is induced by $v$'s neighbor set. We say that $G$ is $(a,b)$-regular for $a>b>0$ integers, if $G$ is $a$-regular and $G_v$ is $b$-regular for every…

Combinatorics · Mathematics 2019-08-29 Michael Chapman , Nati Linial , Yuval Peled
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